Process for producing wood cellulose comparable to cotton, with high tenor of alkali resisting cellulose



Patented Nov. 20, 193 4:

UNITED STATES PROCESS FOR PRODUCING WOOD CELLU- LOSE COMPARABLE TO COTTON, WITH HIGH TENOR F CELLULOSE ALKALI RESISTING Francesco Carlo Palazzo and Fortunato Palazzo, Florence, Italy No Drawing. Application January 23, 1933, Serial 2 Claims.

Various processes are known for obtaining products with a high tenor of alkali resisting cellulose, starting from ordinary sulphite wood cellulose.

These processes however, comprising the use of alkali (such as lime, caustic soda, sodium carbonate or mixtines of same) which are caused to react at ordinary or more or less-elevated temperature, and eventually under pressure, whilst raising the tenor of alkali resisting cellulose offer, on the other hand, some more or less serious drawbacks either because their application requires a long period and costly equipment, or because it involves comparatively high consumption of rell actives and comparatively poor yields of final products, or because such products, whilst nearly similar to cotton by their tenor of alkali resisting cellulose, are inferior to them under various other points of view, for instance by the not sufiiciently high degree of bleaching or the excessively high copper figure or their viscosity somewhat inferior to that of cotton.

Extensive experiments made in the matter have shown that the problem of obtaining from ordinary sulphite wood cellulose a product really comparable with cotton cannot be solved by simply and only using an alkaline treatment capable of solubilizing the hemicellulosic substances. In fact, for certain important uses of wood cellulose as a surrogate of cotton,--in its further treatment for obtaining solutions adapted for the production of artificial textile fibres or films, and particularly in producing ethers and esters of cellulose,also the complete removal of ligninic substances is certainly important, for which, above all, wood cellulose differs from cotton. This removal however cannot be obtained with the alkaline treatment alone even if effected with heat, and requires in turn an oxidizing treatment to be effected with particular considerations if it is desired that the resulting final product should be white and with a low copper content, beneath 1.

, The alkaline and oxidizing treatments must,

furthermore, be strictly coordinated to each other if it is desired, on starting from a common sulphite wood cellulose to obtain a product really comparable to cotton not only as to the title of alkali resisting cellulose, but also to all its other chemical and physical properties.

Characteristic features of process Such strict coordination is realized according to our present invention in the most advantageous way by effecting the alkaline treatment in such conditions as to facilitate at a very notable In Italy December 24, 1932 1. Alkaline treatment This treatment, besides precise conditions of pressure and duration which will be indicated hereafter, is characterized by a particular composition of the alkaline liquor, which latter contains, besides an alkali such as for instance sodium hydrate, sodic salts of a colloidal nature, namely of the class of the emulsoids which are capable of greatly assisting the caustic soda owing to the fact that it disperses in colloidal solution the various substances which the action of this reactive succeeds in detaching from ordinary cellulose. These substances, though referable to very difierent classes of compositions, such as the hemicellulosic substances on the one hand, and the ligninic substances on the other hand, pass under the action of sodic hydrate into colloidal solution as suspensoids, and with respect to them the said emulsoids with their eminent emulsifying power act as protecting colloids which prevent that in the cooling of the lixiviated product they become flocculent at the surface of the fibres, in which case the already effected action of the alkali would be more or less attenuated.

Besides this the use of colloidal substances of the above said type renders superfluous the laborious proceedings following, in certain processes of the kind, the alkaline cookin comprising repeated systematic washings of the cellulose to be refined with alkaline liquors of gradually decreasing concentration. As a matter of. fact, in the washing of the product obtained by the alkaline cooking according to invention the colloidal sodic salts which have remained adhering to the fibres, adsorbed by the latter, become at once,--owing to their hydrolytic scission,-a continuous though feeble source of alkalinity, and this is sumcient for also ensuring the practically complete removal of the resin soap formed in cooking, thereby preserving same from hydrolysis which otherwise would involve precipitation of the free resinic acids on the fibres.

In fine, another significant advantage of the use of the above said sodic salts in addition to caustic soda consists in the fact that owing to the eminent detergent power they facilitate the adsorption of the soda by thefibrous material, and this is economically very advantageous for the process both owing to the short cooking period which may be only two hours, and owing to the high yield of product obtained, because the cellulose is saved from the destructive action of prolonged alkaline cooking.

2.. Omidizing treatment Whilst the alkaline treatment is mainly for removing the hemicellulosic and fat and resinous substances, being only capable of partially solubilizing the lignin components, for the complete removal of these components the use of an oxidant is necessary. However, according to invention, the oxidants are used in such conditions of concentration, temperature and reaction of medium as to react exclusively on the lignin or, at least, so as not to appreciably affect the cellulose.

The oxidizing treatment according to invention is most strictly coordinated with the alkaline treatment owing to the fact that, whilst a portion of the lignin originally contained in the ordinary cellulose is dispersed in' the alkaline liquor and kept therein by its emulsoids, removal' of remaining portion is materially facilitated by the high degree of detersion obtained for the cellulosic material by cooking, and which gives it a very high hydrophilous power. If, therefore, the alkaline cooking according to invention acts mainly to raise the tenor of the alkali resisting' cellulose, it acts at the same time as a very efficient preparation for bleaching and materially contributes to the cheapness, of the process, having for its effect to limit consumption of oxidants and sensibly accelerating bleaching.

In turn, the very favorable bleaching conditions created by the alkaline cooking according to invention, especially the. fact of using only moderate quantities of oxidants remaining for a comparatively short period in contact with the cellulose whilst permitting of obtaining high grade bleaching at a low cost, give a product with a comparatively low copper content, which is always lower than 1.

This does not exclude that bleaching according to invention has its-own characteristic features which consistinjheicombined use of two different oxidants both used at ordinary temperature and rather strongly diluted, but each in particular conditions of pH; precisely, whilst the greater part of the ligninic components is removed with the use of hypochlorites or sodium peroxide, all of them in a slightly alkaline solution, the remaining portion, which oxidizes more slowly in alkaline solution, is attacked in acid solution with hypochlorous acid or potassium permanganate. The action of this latter oxidant, the use of which is limited to the strictly necessary quantity, is very rapid and selectively brought intothe lignin so as not to alter the cellulose, also owing to its :aer: diluted condition and short period of con- The slight excess eventually used and the manganese oxide eventually deposed on the fibres are decomposed by subsequent treatment with an aqueous solution of sulphurous anhydrid, and this treatment at the same time acts to materally attenuate the contents of mineral substances of the final product.

3. Refining of bleached product The strict coordination of the alkaline and oxidizing treatments may also be established in another sense, namely by further refining following on the bleaching, which refining, however, owing to the characters already possessed by the product bleached according to invention may be obtained with a much milder alkaline treatment.

' As in this case the tenor of alkali .resisting cellulose is no more, or very slightly, to be raised, but as it is only necessary to remove a few products of oxidation of lignin still adsorbed by the fibres, as well as the feeble quantity of oxycellulose eventually formed in bleaching, our new treatment is suitably mitigated by associating with the above said emulsoids neutral sodium sulphite instead of caustic soda. In fact, the derivatives of lignin which still are adhering to the fibres are easily dissolved in that reactive, whilst for bringing into the solution the small quantities of oxycellulose, the slight hydrolytic alkalinity of the said emulsoids with which also their high emulsive power is cooperating, will be suflicient.

Technicality of process and characters of product The industrial application of our process offers no difiiculty of any kind and has no special requirements, not even as regards equipment, whilst as a matter of fact the highest refining may be obtained with the equipment of the most modest cellulose factory. The process, furthermore, has a very great flexibility which permits of inserting it into the normal manufacturing of wood cellulose with the bisulphiteprocess (also when applying same in different phases of treatment), and of conforming the characteristic properties of the products, as well as their costs to the more or less valuable purposes for which the said products are designed.

The liquor to be used for the alkaline treatment contains from 1 to 1.5% of sodic hydrate and from 0.2 to 0.3% of colloidal sodic salts, such as sodic soaps of higher fat acids and thei treatment comprises a cooking of a duration of 1 to 2 hours effected at a pressure of 1 to 2 atmospheres in digesters of any, but preferably the rotary type. The cellulose discharged from the autoclave into a lower tank with perforated bottom is drained by dripping for a short period, whereupon it is thoroughly washed out in the usual way and finally subjected to bleaching.

Bleaching is effected in two steps characterized by different reaction of medium, the first 1) being effected in a feebly alkaline medium, and the second 2a, or 2b in a feebly acid medium.

1. On the pulp circulating in the pulper at a concentration not higher than 5 to 6% one causes to react, at ordinary temperature, a solution of hypochlorite (of calcium or sodium) containing from 1.5 to 2% of active chlorine, besides a small quantity of calcium hydrate or sodium carbonate,

or one causes to react a diluted solution, equally alkaline of sodium peroxide.

2a.. 0n the pulp, in the above said conditions of concentration and of temperature one causes to react a solution of hypochlorous acid obtained from that of calcium hypochlorite, by previous 'partial precipitation of lime with carbonic acid or sodium bicarbonate.

21). On the pulp in the above said conditions of concentration and of temperature one causes to react a 1% solution of potassium permanganate containing 2% of sulphuric acid.

Between the oxidation in an alkaline medium and the subsequent oxidation in an acid medium is suitably inserted a washing of the pulp, whilst at the end of bleaching, in whatsoever way it may be effected, to the pulp in movement is furthermore added an approximately 1% solution of sulphurous anhydrid, and the contact extended for about 1 hour, whereupon exhaustive washing is effected when the product will be ready for being reduced to the shapes most adapted for its various uses (such as boards, thin sheets, felts, flakes and so forth).

The further treatment of the bleached product 1 directed to attain a still higher degree of refining comprises heating with a liquor containing 1% of neutral sodium sulphite and 0.25% of the said colloidal sodic salts. The operation may be effected either in autoclave under feeble pressure (0.5 to 1 atm.) or in open vessels at a temperature of to and its duration varies, accordingly, from 1 to 2 hours. On this operation follows, finally. after washing of pulp, also the above said treatment with sulphurous acid.

According to the above described process being stopped at the bleaching in acid solution, or also comprising the treatment with sulphitic liquor. and according to the quality of the starting cellulose, the characteristic features of the finished ,products may vary within the following limits:

Alkali resisting cellulose from -98% Ether soluble substances do 0.15 0.05% Copper figure do 1.0 0.2

Ashes do 0.25- 0.10%

whilst the viscosity value is in everycase very elevated, of the same order as that of cottons, and also their hydrophilous power is similar to that of the best cottons.

It must also be mentioned that the variations of the tenor of alkali resisting cellulose depend, on the other hand, also from the conventional ideas and methods used for analysis. GeneralLv, for a determined tenor of so-called falpha-cellulose" (capable of being valued with varying methods and results), a higher value (of about 1%) will be usually found for the so-called "baryte resisting cellulose".

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is:

1. Process of manufacturing wood cellulose comparable with cotton, with a high tenor of alkali resisting cellulose", characterized in that the cellulose to be refined is treated in autoclave with a liquor containing from 1 to 1.5% of sodic hydrate and from 0.2 to 0.3% of colloidal sodic salts of the emulsoid class, stable with respect to alkalis, at a pressure of 1 to 2 atmospheres and for a period of l to 2 hours.

2. Process as claimed in claim 1. characterizedin that mixtiu'es of sodic soaps of higher fat acids are used as alkali resisting emulsoids.

FRANCESCO CARLO PALAZZO. FORTUNATO PALAZZO. 

